Traditional ballet studios often require a black leotard, pink tights, and pink ballet slippers for ladies and black tights, dance pants, or dance shorts with a fitted white T-shirt and black ballet shoes for men. Dance studios without strict requirements typically recommend wearing clothing made of flexible fabric that hugs tight to the body, so you can move freely and the teacher is able to see your movements and provide feedback.
Since every studio is different, be sure to confirm the dress code guidelines before your first class.